Monoclonal immunoscintigraphy for the detection of primary colorectal cancers: a prospective study

A prospective study to investigate the value of monoclonal antibody (McAb) immunoscintigraphy for the detection of primary tumours of the colon and rectum has been undertaken. Twelve patients received 1 mg 131I-labelled McAb YPC 2/12.1, an antibody raised to a human colonic carcinoma membrane preparation. Imaging of the blood pool was achieved using 99mTc-labelled red cells. After surgery specimens were scanned and samples of normal and malignant tissue excised to obtain antibody binding ratios. In only one patient was the primary tumour visualized pre-operatively. Images of the resected specimens revealed the primary tumour in ten cases but this appeared to be a function of increased blood pool within the tumour rather than specific antibody localization. The mean tumour/normal tissue count ratio was 1.27:1 (range 0.63:1-1.93:1). It is concluded that the McAb YPC 2/12.1 is unlikely to be of use clinically. Furthermore when selecting McAbs for the purposes of immunoscintigraphy the results of in vitro binding to malignant cell lines, immunohistological studies and xenograft experiments may be misleading and careful clinical evaluation is necessary.